Nonlinear conduction elements



Sept 27, 1955 R. K. wlLLARDsoN ET AL 2,719,253

NONLINEAR CONDUCTION ELEMENTS Filed Feb. ll, 1955 IN VEN TORS.

n n m, m d E V d N mam mmm n KOE A nm mmm J RAMA United States Patent l 2,719,253 NONLINEAR CONDUCTIN ELEMENTS Robert K. Willardsou, Albert C. Beer, and Arthur E. Middleton, Columbus, Ohio, assignors, by mesne assignments, to Bradley lVIining Company, San Francisco,

Calif., a corporation of California Application February 11, 1953, Serial No. 3%,298

` 3 Claims. (Ci. 317-237) This invention relates to nonlinear conduction elements. It has'to do, more particularly, with semiconductor devices, such as rectiiiers, in which the semiconductor comprises aluminum antimony.

It is well known that galena, selenium, copper oxide, iron' pyrites, germanium, and various other semiconductors can be used in rectiiiers. While rectifiers madey of such materials are useful for many purposes, they are not generally satisfactory for high-temperature operation. Rectifiers in which' silicon is used as the semiconductor are somewhat better at high temperatures than are those made of the materials mentioned above, but silicon has a high melting point and other disadvantages from the manufacturing standpoint. A

It is a primary object yof the present invention, 'therefore, to provide a semiconductor-type rectier that is inexpensive, easily fabricated, and capable of operation at high temperatures, such as temperatures in excess of 200 C It is also an object of this invention to provide a rectifier having as its semiconductor material the compound aluminum antimony, a material having a relatively low melting point, yet having a large band separation or energy gap as is required for such high-temperature operation.

The foregoing and other objects and advantages are provided by the invention disclosed herein.

In the drawings:

Fig. l is a graph illustrating a representative voltagecurrent characteristic curve of a low-resistance P-type rectier, the semiconductor element of which is made of the compound aluminum antimony in accordance with the present invention;

Fig. 2 is a similar graph illustrating a representative voltage-current characteristic curve of a medium-resistance P-type rectifier having an aluminum antimony semiconductor element in accordance with the present invention;

Fig. 3 is a similar graph illustrating a typical rectifying characteristic curve of a `high-resistance P-type rectifier according to this invention;

Fig. 4 is a similar graph illustrating a typical rectifying characteristic curve of an N-type rectifier having a semiconductor element of aluminum antimony according to the present invention; and

Fig. 5 is a perspective View, partially schematic, of a typical rectifier, the semiconductor of which is made of aluminum antimony in accordance with the present invention.

A rectifier according to the present invention comprises a semiconductor and an electrode or Whisker, the electrode making contact with a surface of the semiconductor, and the semiconductor comprising the compound aluminum antimony. This compound preferably is formed by reacting aluminum and antimony with the elements present in the proportions of substantially 50 atomic per cent aluminum and substantially 50 atomic per cent antimony. For best results, the proportions should be from about 49.5 to about 50.5 atomic per cent aluminum and from about 50.5 to about 49.5 atomic per cent antimony. In general, impurities preferably are limited to not more than about one atomic per cent. impurities comprising elements in the same column of the periodic Vtable as aluminum, which are referred to herein as aluminum-type impurities, however, may be tolerated in ice amounts of up to about ten atomic per cent if such impurities replace substantially an equal total atomic per cent of aluminum so that the aluminum and these impurities together comprise substantially 50 atomic per cent of the compound. Also, impurities comprising elements in the same column of the periodic table as antimony, which are referred to herein as antimony-type impurities, may be tolerated in amounts up to about ten atomic per cent if such impurities replace substantially an equal total atomic per cent of antimony so that the antimony and these impurities together comprise substantially 50 atomic per cent of the compound. Although for best results impurities should be carefully controlled, aluminum-type impurities up to about ten atomic per cent, antimony-type impurities up to about ten atomic per cent, and other impurities up to about one atomic per cent may all be tolerated if the aluminum plus aluminum-type impurities comprise substantially 50 atomic per cent of the compound and the antimony plus antimonytype impurities comprise substantially 50 per cent of the compound.

The aluminum-antimony semiconductor as used in rectiliers according to this invention is characterized by high resistanceto electric current in one direction therethrough and low resistance to electric current in the opposite direction therethrough. In one type of aluminum antimony rectifier, a high resistance to the electric current is provided when the contacting electrode is positive and the semiconductor is negative, and a low resistance to the electric current is provided when the contacting electrode is negative and the semiconductor is positive. In other words, the aluminum antimony in the aforementioned rectitier is in such a form that it is a P-type semiconductor. Controlled impurities, such as a small excess of antimony, may be added, however, so that the aluminum-antimony compound is produced as an N-type semiconductor, if desired. In such case, a high resistance to electric current is provided when the contacting electrode is negative and the semiconductor is positive, and a low resistance to electric current is provided when the contacting electrode is positive and the semiconductor is negative. While a precise dividing line has not been detinitely established, it appears that a small excess of aluminum, or of aluminum plus other aluminum-type impurities in the aluminumantimony compound provides a P-type semiconductor; and that a small excess of antimony, or of antimony plus other antimony-type impurities, provides an N-type semiconductor. Substantially pure aluminum antimony provides a band separation or an energy gap of at least about one electron volt, and thus has useful rectiiier properties and other useful semiconductor properties over a wide temperature range. Rectiiiers according to the present invention, therefore, are useful at high temperatures.

It has been found as a part of the present invention that the two metals, aluminum and antimony, each a reasonably good conductor of electricity, when combined in the stoichiometric proportions to obtain the compound aluminum antimony, form a semiconductor material having many useful properties such as those illustrated in the drawings, rather than a conductor, as might ordinarily be expected. i

One method of preparing :aluminum antimony having desirable semiconductor properties comprises placing aluminum metal and antimony metal in the proportions of substantially 50 atomic per cent aluminum and 50 atomic per cent antimony in a graphite Crucible, or other container made of a material that will not react with either of the metals, and reacting the metals by zone melting in an induction furnace. The metals should be thoroughly reacted while molten. Then the material may be cooled. Impurities should be carefully controlled, as discussed above, and the portion of the resulting compound in contact with the container, as well as the last portion of the melt .to solidify which vis likely .to have i additional impurities diffused therein should be discarded, and only the substantially pure central portion of the mass should be used as the semiconductorfin a rectifier according to the present invention. The substantially pure aluminum antimony obtained in the central portion of the reacted material may be used in a contact-type rectifier to provide voltage-current characteristics as illustrated in Figs. 1 through 4.

Figs. l and 2 show the rectifying characteristics of typical low-resistance and medium-resistance rectiers, respectively, made from P-type aluminum antimony. The aluminumantimony used in the rectifier having the higher back voltage and higher resistance characteristics (Fig. 2) has slightly higher purity than vthe aluminum antimony used in the first example (Fig. 1). Lowresistance rectifiers are useful in low-impedance circuits where the impressed signals are ordinarily limited to tWo volts or less. It is to be noted from Fig. 1 that for impressed signals near one volt applied to a typical lowresistance, aluminum-antimony rectifier ratios of forwardto-back currents greater than 1000 are easily obtained. From Fig. 2, it is apparent that forward-to-back ratios in the neighborhood of 1500 are obtainable with a typical medium-resistance aluminum-antimony rectifier .for one volt of impressed signal.

Fig. 3 shows the rectifying characteristics of a higher resistance rectifier made from P-type aluminum antimony of still higher Vpurity than that used in the rectifier of Fig. 2. It is to be noted that the rectifier of Fig. 3 provides useful rectification characteristics over a wide range of voltages, with forward-to-back ratios of approximately 100 for impressed signals between one and 2O volts.

Fig. 4 shows the characteristics of a rectifier made from N-type valuminum antimony. Forward-to-back ratios in the neighborhood of 65 are provided at one volt.

The rectifying characteristics of Figs. l through 4 can be improved by known techniques, such as electrical forming, etching and other special surface treatment, ionic bombardment, and mechanical agitation, if desired.

Fig. 5 illustrates la typical formof contact-type rectifier having a semiconductor made of the compound aluminum antimony, as disclosed herein. An electrode or cat Whisker V11 is provided with a pointed end 12 which makes point contact .with the upper surface 13 of the semiconductor 10 to provide a rectifying junction. The electrode 11 should bemade of a good electrical conductormaterial, such as a metal or a metal alloy. Copper, nickel, platinum, tungsten, and other suitable conductor materials may be used. The end 12 of the electrode 11 should have a sharp contacting end of diameter, in the neighborhood of 0.001 inch, while the remainder ofthe electrode il'lmay be considerably thicker to provide good mechanical strength. An electrical conductor 14 may be soldered, swaged,.or welded to the electrode 11, as is indicatedat I15, for connection to any suitable circuit in which it is desired to connect the rectifier. The lower surface 16 of the semiconductor 10 is soldered or electrically connected by other suitable means to a conductor plate 17, whichmay be made of any good electrical conductor material, such as a suitable metal or metal alloy. Anelectrical conductor 18 may be-soldered to the conductor plate 17, as is indicated at 19, for connecting the rectifier to a suitable circuit in Awhich `it is desired to be connected. Rectifiers made as illustrated in Fig. 5, or in various equivalent ways that will be apparent to -those skilled in the art, using aluminum `antimony as the semiconductor in accordance .with the present invention, will provide good .rectifying characteristics, such as those illustrated in Figs. 1 through 4.

From the foregoing disclosure, itis apparent that inexpensive, easily manufactured, semiconductor-type rectiers have Vbeen provided using the compound valuminum antimony as the semiconductor. Semiconductor materials made in accordance with the present invention are characterized by a large band separation or energy gap and provide useful semiconductor properties even at high temperatures. By the additionfof a controlled impurity or impurities, such as a slight excess of antimony or other antimony-type impurities, the aluminum antimony may be made as an N-type semiconductor material. By the addition of a different type of controlled impurity yor impurities, such as a slight excess of aluminum or other aluminum-type impurities, the aluminum antimony may be made as a P-type semiconductor material. It will be understood,lof course, that, While the forms of the invention herein shown and described, constitute preferred embodiments of the invention, it is not intended herein to illustrate all of the possible equivalent forms or ramifications of the invention. It will also be understood that the words used are words of description rather than of limitation, and that various changes, such as changes in shape, relative size, and arrangements of parts, may be substituted without departing from the spirit or scope of the invention herein disclosed.

What is claimed is:

l. A rectifier comprising a semiconductor and an electrode making contact with a surface of said semiconductor, said semiconductor consisting predominantly of the material formed by reacting total atomic per cent of at least one element of group III of the periodic table, including at least 40 atomic per cent aluminum, 50 total atomic per cent of at least one element of group V of the periodic table, including at least 40 atomic per cent antimony, and a slight additional amount of at least one material selected from the group consisting of the elements of group III of the periodic table and the elementsof group V of the periodic table, all of said additional amount of elements being selected from the same group of the periodic table.

2. A rectifier comprising a semiconductor and an electrode making contact with a surface of said semiconductor, said semiconductor consisting predominantly of the material formed'by reacting 50 total atomic per cent of at least one element of group III of the periodic table, including at least 40 atomic per cent aluminum, 50 total atomic per cent of at least one element of group V of the periodic table, including at least 40 atomic per cent antimony, and a slight additional amount of at least one element of group III of the periodic table, the rectifier having a higher resistance to the electric current when the electrode is positive and the semiconductor is negative and a lower resistance to the electric current when the electrode is negative and the semiconductor is positive.

3. A rectifier comprising a semiconductor and an electrode making contact with a surface of said semiconductor, said semiconductor consisting predominantly of the material formed by reacting 50 total atomic per cent of at least one element of group III of the periodic table, including at least 40 atomic per cent aluminum, 50 total atomic per cent of at least one element of group V of the periodic table, including at least 40 atomic per cent antimony, and a slight additional amount of at least one element of group V of the periodic table, the rectifier having a higher resistance to the electric current when the electrode is negative and the semiconductor is positive and a lower resistance to the electric current when the electrode is positive and the semiconductor is negative.

References Cited in the file of this patent lished in Zeitschrift vfur Naturforschung, vol. 7a, pp. 744-749.

Examinable in 

1. A RECTIFIER COMPRISING A SEMICONDUCTOR AND AN ELECTRODE MAKING CONTACT WITH A SURFACE OF SAID SEMICONDUCTOR, SAID SEMICONDUCTOR CONSISTING PREDOMINANTLY OF THE MATERIAL FORMED BY REACTING 50 TOTAL ATOMIC PER CENT OF AT LEAST ONE ELEMENT OF GROUP 111 OF THE PERIODIC TABLE, INCLUDING AT LEAST 40 ATOMIC PER CENT ALUMINUM, 50 TOTAL ATOMIC PER CENT OF AT LEAST ONE ELEMENT OF GROUP V OF THE PERIODIC TABLE INCLUDING AT LEAST 40 ATOMIC PER CENT ANTIMONY, AND A SLIGHT ADDITIONAL AMOUNT OF AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF THE ELEMENTS OF GROUP 111 OF THE PERIODIC TABLE, AND THE ELEMENT MENTS OF GROUP V OF THE PERIODIC TABLE, ALL OF SAID ADDITIONAL AMOUNT OF ELEMENTS BEING SELECTED FROM THE SAME GROUP OF THE PERIODIC TABLE. 